A weed is generally defined as a plant growing where it is not required. Destruction of weeds can be by a number of means; physical removal, covering, herbicidal chemicals, burning, or scalding with hot water, steam, or both. These methods have their own particular disadvantages for particular applications; for example herbicidal chemicals may leave residues harmful to other life forms or drift from the target plant on to a valuable plants. Burning can start destructive fires.
The preferred method; using hot water, does not leave residues and although it does require energy at the point of use there is no particular energy requirement involved in supplying the raw material: water.
There is a good deal of merit in minimizing the amount of heat energy used by a hot-water applicator means, because water has a high specific heat and the act of boiling water consumes even more heat. Energy consumption is always seen as a disadvantage of hot-water weed control though it must be remembered that it is highly visible whereas the energy cost of preparing or disposing of a weed killer is invisible.